This invention concerns a method of manufacturing polyester fibers with good adhesiveness to rubber.
Polyester fibers, represented by polyethylene terephthalate, are fibers with excellent physical and chemical properties; they are produced industrially in large quantities and are very useful in various fields. They are also extremely useful as reinforcing materials for rubber.
However, when compared with polyamide fibers such as nylon 6, nylon 6,6, etc., which are other typical industrial fibers, polyester fibers have the great defect that they are inferior in adhesiveness to rubber.
That is, polyamide fibers become fibers with very good adhesiveness to rubber simply by being treated with a resorcinol-formalin-latex rubber (RFL) adhesive agent, but in the case of polyester fibers good adhesiveness cannot be obtained even with the RFL treatment.
For this reason, many attempts have been made for some time to improve the adhesiveness of polyester fibers with rubber. Typical of such methods is the method in which, when the raw cord fiber is RFL-treated (the so-called "dipping" treatment), it is first pretreated with an adhesive agent such as an epoxy compound, as isocyanate compound, or an ethylene urea compound, etc., or it is dip treated with RFL which contains an esterophilic ingredient such as a novolak resin, 2,6-bis(2',4'-dihydroxyphenyl methyl-4-chlorophenol, known by the trade name "Pexul"; or the method in which at the yarn stage an adhesive agent such as an epoxy compound, an isocyanate compound, or an ethylene urea compound, etc., is added, and it is then dip-treated with RFL. The former method, while the desired adhesiveness is obtained to some extent, has the defect that it causes an increase in cost because the quantity of adhesive agent used is large, the treatment method is complicated and troublesome, etc. The latter method has the practical advantage that the later dipping treatment can be performed with RFL alone, as in the case of polyamide fibers, but it has the defect that the desired adhesive function is somewhat unsatisfactory. Consequently, particularly in the case of the latter method, a new problem is caused in that the method of treating the yarn itself must be performed in such a way that it greatly deviates from the practical range in order to increase the adhesive function. The concentration of the adhesive agent in treating the yarn is markedly increased, the heat treatment conditions are made extremely severe, etc.